1. Field of the Invention
The present invention relates generally to a method of and a device for transmitting print data in the data transmission mode of the device to a print control device for controlling a printer, and also relates to such print control device. More particularly, this invention is concerned with a technique for partial replacement or change of image data included in the original print data before transmission of the changed image data to the print control device together with print control data changed so as to meet the partial replacement of the print data. The invention is also concerned with a technique for efficient transmission of the print data from a device such as a word processor incorporating a computer, and efficient processing of the print data received by the print control device.
2. Discussion of the Prior Art
A printing system is known, wherein a print control device is interposed between a computer (e.g., a computer built in a word processor) and a printer, for controlling the printer according to print data received from the computer. Generally, the print data include image data directly or indirectly representing images to be printed, and print control data including attribute data as well known in the art. The image data include direct image data such as bit map data, which are generated on the basis of an output of an image scanner, for example. The direct image data also include data obtained by compression of such bit map data. Such compressed direct image data may include, for instance, run-length codes well known in the art. The image data also include indirect image data such as character data or character codes representative of characters such as letters, symbols and numerals, and graphic data representative of graphic or pictorial representations including straight and curved lines. The graphic data may be referred to as "outline data" representative of outlines of images to be reproduced.
The known printing system of the type indicated above suffers from a problem when the user desires to partially replace or change the image data included in the original print data already prepared by and stored in the computer, after the computer is set in its data transmission mode. Namely, the entire print data should be prepared again even when the image data in the original print data are partially replaced by other image data. It takes a considerable time to edit the original print data in the data transmission mode of the computer. Usually, the print data include a large volume of image data, and a lot of time is required for the appropriate application program to read the entire volume of the print data during processing for partial change or replacement of the image data. Further, the change or replacement of the image data itself requires a large length of time. Thus, an operation to partially change or replace the original image data leads to reduced efficiency of the printing system. In some cases, the application program does not permit partial editing of the original print data, that is, requires preparation of an entirely new batch of print data as desired by the user.
The print control device used in some printing systems is adapted to use a page description language. In this type of printing system, the image data and the print control data which are included in the print data are transmitted from the computer to the print control device such that the image data and the print control data are interspersed with each other. The print control device converts each one-page portion of the print data received from the computer into a batch of raster image data, according to the print control data such as attribute data and various print control instructions. Each batch of raster image data is sent to the printer for printing of the corresponding page.
Keeping pace with recent enhancement of resolution of an image input or reading device such as an image scanner, the amount of the direct image data in the form of bit map data, for instance, tends to increase per unit area of the image. This means an increase in the total volume of the print data, and the print control device is required to search for the print control commands or instructions mixed or dispersed in the large volume of the bit map data, so that the bit map data are converted into the raster image data according to the print control commands or instructions. Therefore, the efficiency of processing of the print data by the print control device tends to be lowered, and the time required for the computer to transmit the print data to the print control device tends to increase due to the relatively low processing efficiency on the side of the print control device.